DESCRIPTION Floating point numbers can have special
values, such as infinite or NaN. With the macro
fpclassify(x) you can find out what type x is. The macro
takes any floating-point expression as argument. The result
is one of the following values:

FP_NAN x is "Not a Number".

FP_INFINITE x is either positive infinity or negative
infinity.

FP_ZERO x is zero.

FP_SUBNORMAL x is too small to be represented in
normalized format.

FP_NORMAL if nothing of the above is correct then it
must be a nor- mal floating-point number.